For example, compared to Hispanic/Latina women and Black/non-Hispanic black/African-American women, white/non-Hispanic white women are more likely to have children at a later age and to have fewer children [11,264,266-271]. These factors increase breast cancer risk [11].

Compared to Hispanic women, non-Hispanic white women are also more likely to use menopausal hormone therapy and less likely to breastfeed [266]. Each of these factors also increases breast cancer risk [11].

The reasons behind these differences are under study. They may include differences in prevalence rates of some reproductive and lifestyle factors related to breast cancer risk as well as differences in tumor biology [264-271].

Age at diagnosis

Black women tend to be diagnosed at a younger age than white women [5].

The median age at diagnosis for black women is 59, compared to 63 for white women [5].

Thus, although African-American women may be more likely than white women to have these protective factors, they may not lower the risk of triple negative breast cancers as much as they lower the risk of ER-positive cancers.

For example, Black/African-American women are more likely than white/non-Hispanic white/Caucasian women to [112,268,278-279]:

Have more children

Be a younger age at first childbirth

Be overweight or obese before menopause

Although these factors lower the risk of breast cancer, this benefit may be limited to ER-positive breast cancers [69-70,112,268,278]. There's even some evidence these factors may increase the risk of triple negative breast cancers [69-70,112,268,278].